Bring 1/4-inch water with a splash of white wine to a boil in a small sauce pan. Add mussels, cover, and steam until just open, about 2-3 minutes. Remove mussels with slotted spoon (discard any that don’t open) and when cool, remove from shells, coarsely chop and set aside.Combine the fish stock and milk in a large pot and bring to a simmer. Add the mixed vegetables and simmer until just beginning to soften, about 6-8 minutes.

Add the fish and shrimp and simmer until almost cooked through, about 3-4 minutes. Stir in the cream, then slowly stir in the flour/water mixture to thicken. Simmer for 5 minutes to combine flavors.

Add mussels, season to taste with salt and pepper, and serve in soup bowls garnished with a wedge of lemon.